With lifestyle changes in diet, smoking, and stress following industrialization and economic growth, the occurrence of vascular diseases such as atherosclerosis has increased rapidly. For their treatment, noninvasive interventional procedures such as percutaneous transluminal coronary angioplasty and stenting have been applied. However, the recurrence rate of vascular diseases after percutaneous transluminal coronary angioplasty is very high. Stenting can significantly lower the recurrence rate compared with traditional angioplasty and has therefore been applied more often in the recent years.
However, stenting entails several safety concerns, the most serious of which is stent thrombosis. Stent thrombosis is blood clot formation inside a stent, leading to myocardial infarction or sudden cardiac death. As this condition generally occurs more than one year after stent implantation, temporary scaffolding of blood vessel walls is required to reduce the risk of thrombosis following stent biodegradation at the implant site.
Poly(L-lactide) (PLLA) is a bioabsorbable polymer hydrolyzing into lactic acid under aqueous conditions. High-molecular-weight PLLA is known to be an adequate material for temporary scaffolding of blood vessel walls due to its relatively slow biodegradability and strong mechanical properties with respect to blood vessel walls.
U.S. Patent Publication No. 2005/0208093 discloses a composition comprising phospholipids such as phosphorylcholine, which are useful for coating of implantation devices such as drug-eluting stents. Further, U.S. Pat. No. 5,712,326 states that the biocompatibility of various polymers is improved by blending with a polymer including a zwitterionic group.
However, these conventional techniques require the coating of a metallic platform with a bioabsorbable polymer. Moreover, the conventional coating of the platform with PPCP was not efficient, which phosphorylcholine groups are not detected on the surface of conventional PPCP coated stents by an X-ray photoelectron spectroscope (XPS).
The inventors of this invention conducted various studies to solve such problems of the conventional techniques and were able to complete an invention that permits biodegradation of the stent while improving mechanical strength.